Re: WMATA crash & track circuits

On Sat, 26 Sep 2009 15:44:38 -0700, Joerg <invalid@xxxxxxxxxxxxxxx>
wrote:

Jan Panteltje wrote:
On a sunny day (Sat, 26 Sep 2009 12:37:23 -0700) it happened Joerg
<invalid@xxxxxxxxxxxxxxx> wrote in <7i78ruF2urvmlU1@xxxxxxxxxxxxxxxxxx>:

<clip>

Well, have you ever worked in industrial electronics, aerospace, oil?

Industrial yes, oil yes, aerospace not directly.


Then how on earth did you get away with 10 years service life designs?


In normal industrial applications, it is seldom required that each and
every component will last for decades. If a system is critical for
plant operation, double or triple redundancy is often used, so there
are usually a few days time to replace a failed subsystem.

For plants that are going to function for decades, it is important to
have a stable control system architecture, in which the plant system
can be extended with compatible subsystems which are implemented with
radically different (more modern) hardware.

If the architecture is stable enough, you can even remove the racks of
central parts of a 10-20 year old system and replace with new racks
and connect the cables in one or two days. Plants usually require
shutdowns at least every few years for mechanical engineering
overhaul, so the control system can be upgraded without extra loss of
production.

However, when planning for extended (10-40 years) life cycles require
quite conservative design. You can not design for a single source
fancy processor card with all the peripherals you might want. It is
quite likely that such cards will not be in production after a few
years, the card vendor might go bankrupt or bought by a competitor.
These days the RoHS directive will cause the end of life of some
products that otherwise would have been in production for years.

For this reason, passive backplanes have been quite popular, so that
single function (often with multiple interfaces) cards can be used
from whichever vendor might produce suitable cards for some years,
which era hopefully will partly overlap with cards from different
vendors.

Paul

.

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